LIMITATIONS OF VENTRICULAR LATE POTENTIALS IN ATRIAL-FIBRILLATION

It is generally admitted that the chaotic atrial activation in atrial fibrillation makes analysis of ventricular late potentials uninterpretable. However, some workers have contradicted this affirmation. The authors performed signal averaged electrocardiogram in 17 patients with atrial fibrillation before cardioversion for external D.C. shock. The recording was repeated 15 minutes after restoration of sinus rhythm. None of the patients had complete bundle branch block in atrial fibrillation or sinus rhythm. Analysis was made with a band pass filter of 40 Hz and to a final noise level of 0.3 muV. The positivity of late ventricular potentials was confirmed by the presence of at least 2 of the usual 3 criteria: an averaged QRS duration > 120 ms, a RMS 40 < 20 muV and a LAS > 40 ms. The mean duration of the averaged filtered QRS complex was 122 ms in atrial fibrillation and 112 ms in sinus rhythm, a non significant decrease of 9 %. The mean value of the RMS 40 was 24 mu V before cardioversion versus 29 muV after restoration of sinus rhythm, a significant increase of 19% (p < 0.05). Finally, the mean duration of the LAS in atrial fibrillation was 45 ms, decreasing to 35 ms in sinus rhythm, a significant reduction of 22 % (p < 0.05). In atrial fibrillation, 10 patients had ventricular late potentials (2 positive criteria) and 7 had no ventricular late potentials. In sinus rhythm, on the other hand, 6 patients were positive and 11 negative. Therefore, after restoration of sinus rhythm, there was a tendency to shortening of the QRS duration and of the LAS and to an increase of the RMS. Of the 10 patients with ventricular late potentials in atrial fibrillation, 4 patients were negative after restoration of sinus rhythm. On the other hand, none of the negative patients became positive. Atrial fibrillation may therefore result in false positive results of ventricular late potentials but cannot cause any false negative results. In atrial fibrillation, the detection of ventricular late potentials has less positive predictive value than in sinus rhythm but it keeps its negative predictive value.